Hadean protocrust reworking at the origin of the Archean Napier Complex (Antarctica)
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Keywords: Hadean-Archean, zircon U-Pb geochronology, Lu-Hf isotopes, 143,142Nd isotopes, Napier Complex
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 Figure 1 Cathodoluminescence images of representative crystals from Napier zircon populations with details of textures with and without annealing. This figure illustrates the CL signal enhancing effect of zircon annealing which, in turn, allows three groups to be identified based on internal textures (see text for details). Thick white bars represent 50 μm. |  Figure 2 ɛHf versus 207Pb/206Pb age diagrams for Mount Sones and Gage Ridge zircons. Black dashed lines represent the time-evolution of a CHUR reservoir (Iizuka et al., 2015) formed at 4568 Ma (Bouvier and Wadhwa, 2010). Black dotted lines correspond to reservoirs that started with group 1 initial 176Hf/177Hf and evolved with 176Lu/177Hf ratios that are indicated on the left of the diagrams (e.g., 0.025). The values of 0.002 and 0.0016 correspond to 176Lu/177Hf measured in whole rock powders of Mount Sones and Gage Ridge orthogneisses, respectively. The grey fields encompass evolutions of Napier zircons based on highest and lowest 176Lu/177Hf measured in Mount Sones and Gage Ridge zircon populations. The general positive correlation of data for group 1 highlights typical artefacts of ancient Pb loss (e.g., Guitreau et al., 2012). Therefore, the original Hf isotope signatures of corresponding zircon populations are indicated by the oldest (and most concordant) crystals, which happen to be sub-chondritic for both samples. Data are fully consistent between annealed and not-annealed zircons, hence, demonstrating that annealing did not influence any of the measured systematics. |  Figure 3 Coupled 146Sm-142Nd and 147Sm-143Nd plot showing the data obtained for Mount Sones orthogneiss (78285007) as well as the coupled evolution of μ142Nd and ɛ143Nd signatures for lithologies with various Sm/Nd ratios. Solid lines represent isochrons with respective ages indicated by ∆T, which means time after 4568 Ma. Dashed curves correspond to the coupled evolution of μ142Nd and ɛ143Nd signatures according to specific 147Sm/144Nd values that are indicated next to the curves (i.e. 0.14-0.19). Mount Sones μ142Nd and ɛ143Nd isotope signatures are compatible with a mafic source (147Sm/144Nd = 0.17) that separated from a reservoir with a chondritic REE pattern ~150 Myr after Solar System formation (i.e. ~4400 Myr ago). Here we assume that the initial 142Nd/144Nd ratio of the Earth is similar to that measured in the modern terrestrial mantle (μ142Nd = 0), which is equivalent to the signature measured in enstatite chondrites from the EL sub-group (Boyet et al., 2018). |
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Letter
The small number of localities hosting >3.7 Ga rocks, together with the absence of Hadean rocks from the geological record, is a limitation for our understanding of the early evolution of the Earth and the origin of the first continents (e.g., Condie, 2007
Condie, K. (2007) The distribution of Paleoarchean crust. In: Van Kranendonk, M.J., Smithies, R.H., Bennett, V.C. (Eds.) Earth’s Oldest Rocks. First Edition, Elsevier, Amsterdam, 9-18.
). The high metamorphic grade experienced by some of these Archean terranes further represents a challenge to uncover reliable information from their rocks and minerals. The Napier complex (East Antarctica) is one of the few Archean terranes that contain some of Earth’s oldest rocks (Black et al., 1986Black, L.P., Williams, I.S., Compston, W. (1986) Four zircon ages from one rock — the history of a 3930 Ma-old granulite from Mount Sones, Enderby Land, Antarctica. Contributions to Mineralogy and Petrology 94, 427–437.
; Fig. S-1). This complex recorded Meso- and Neoarchean metamorphism that reached extreme conditions corresponding to granulite facies at 2.5 Ga (1050-1120 °C and 7-11 kbar; Table S-1) (Harley and Motoyoshi, 2000Harley, S.L., Motoyoshi, Y. (2000) Al zoning in orthopyroxene in a sapphirine quartzite: evidence for >1120°C UHT metamorphism in the Napier Complex, Antarctica, and implications for the entropy of sapphirine. Contributions to Mineralogy and Petrology 138, 293-307.
). Consequently, radiogenic isotope systematics (e.g., Rb-Sr, Sm-Nd) were severely disturbed in most samples (e.g., Black and McCulloch, 1987Black, L.P., McCulloch, M.T. (1987) Evidence for isotopic equilibration of Sm-Nd whole-rock systems in early Archaean crust of Enderby Land, Antarctica. Earth and Planetary Science Letters 82, 15-24.
). Metamorphic events were recorded in zircon crystals that sometimes also preserved information about original crystallisation (Kelly and Harley, 2005Kelly, N.M., Harley, S.L. (2005) An integrated microtextural and chemical approach to zircon geochronology: refining the Archaean history of the Napier Complex east Antarctica. Contributions to Mineralogy and Petrology 149, 57-84.
). These grains show a greater complexity than commonly seen in ancient zircons (Williams et al., 1984Williams, I.S., Compston, W., Black, L.P., Ireland, T.R., Foster, J.J. (1984) Unsupported radiogenic Pb in zircon: a cause of anomalously high Pb-Pb, U-Pb and Th-Pb ages. Contributions to Mineralogy and Petrology 88, 322-327.
; Black et al., 1986Black, L.P., Williams, I.S., Compston, W. (1986) Four zircon ages from one rock — the history of a 3930 Ma-old granulite from Mount Sones, Enderby Land, Antarctica. Contributions to Mineralogy and Petrology 94, 427–437.
; Guitreau et al., 2012Guitreau, M., Blichert-Toft, J., Martin, H., Mojzsis, S.J., Albarède, F. (2012) Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust. Earth and Planetary Science Letters 337, 211-223.
; Kusiak et al., 2013Kusiak, M.A., Whitehouse, M.J., Wilde, S.A., Nemchin, A.A., Clark, C. (2013) Mobilization of radiogenic Pb in zircon revealed by ion imaging: implications for early Earth geochronology. Geology 41, 291–294.
; Hiess and Bennett, 2016Hiess, J., Bennett, V.C. (2016) Chondritic Lu-Hf in the early crust-mantle system as recorded by zircon populations from the oldest Eoarchean rocks of the Yilgarn Craton, West Australia and Enderby Land, Antarctica. Chemical Geology 427, 125-143.
) and deconvoluting original igneous signatures from metamorphic overprints remains challenging. This is particularly well-illustrated by the great dispersion of data points in εHf versus age space (Fig. S-2 and Table S-2). More importantly, the oldest signatures overlap enriched (negative εHf values) and depleted (positive εHf values) domains, hence, leaving open contrasting possibilities for the nature of the source to these ancient rocks. The analytical methods employed in previous studies do not allow these complexities to be understood, which justifies the present contribution.Here we combine cathodoluminescence (CL) and back scattered electron (BSE) images with U-Pb age profiles by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in zircons from two Napier orthogneisses, following the procedure outlined in Guitreau et al. (2018)
Guitreau, M., Mora, N., Paquette, J.-L. (2018) Crystallization and disturbance histories of single zircon crystals from Hadean-Eoarchean Acasta gneisses examined by LA-ICP-MS U-Pb traverses. G-Cubed 19, 272-291.
. We also measured Lu-Hf isotope systematics by LA-MC-ICP-MS within the same zircon crystals. Finally, we analysed 146,147Sm-143,142Nd isotope systematics in corresponding whole rock samples to constrain the early history of their source better. Information regarding analyses and results are provided in Methods (see Supplementary Information and Tables S-3 to S-11). The two studied samples are granulitic orthogneisses labelled 78285007 (Mount Sones) and 78285013 (Gage Ridge). They are among the oldest rocks from this area (Black et al., 1986Black, L.P., Williams, I.S., Compston, W. (1986) Four zircon ages from one rock — the history of a 3930 Ma-old granulite from Mount Sones, Enderby Land, Antarctica. Contributions to Mineralogy and Petrology 94, 427–437.
; Harley and Black, 1997Harley, S.L., Black, L.P. (1997) A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies. Antarctic Science 9, 74-91.
). Mount Sones exhibits chemical composition identical to that of typical Archean tonalite-trondhjemite-granodiorite (TTG) suites (e.g., high Na2O/K2O, high Sr/Y, fractionated REE patterns; Moyen and Martin, 2012Moyen, J.-F., Martin, H. (2012) Forty years of TTG research. Lithos 148, 312-336.
) with a normative composition intermediate between tonalite and trondhjemite (Black et al., 1986Black, L.P., Williams, I.S., Compston, W. (1986) Four zircon ages from one rock — the history of a 3930 Ma-old granulite from Mount Sones, Enderby Land, Antarctica. Contributions to Mineralogy and Petrology 94, 427–437.
; Fig. S-3). Gage Ridge has a composition closer to that of granite (Harley and Black, 1997Harley, S.L., Black, L.P. (1997) A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies. Antarctic Science 9, 74-91.
) despite a strongly fractionated REE pattern with a pronounced positive Eu anomaly suggesting that it is likely a cumulate from a TTG melt (Fig. S-3).Napier zircon crystals have experienced a complex geological history which is difficult to decipher given their high U and Th concentrations that are responsible for the faint signals in CL images (e.g., Kusiak et al., 2013
Kusiak, M.A., Whitehouse, M.J., Wilde, S.A., Nemchin, A.A., Clark, C. (2013) Mobilization of radiogenic Pb in zircon revealed by ion imaging: implications for early Earth geochronology. Geology 41, 291–294.
). These issues prevented internal textures to be examined properly in previous studies as shown in Figure 1 (see also Figs. S-4 to S-7). We performed annealing on a subset of zircon crystals (850 °C for 48 hr) because this thermal process increases the intensity of the CL signal (Nasdala et al., 2002Nasdala, L., Lengauer, C.L., Hanchar, J.M., Kronz, A., Wirth, R., Blanc, P., Kennedy, A.K., Seydoux-Guillaume, A.-M. (2002) Annealing radiation damage and the recovery of cathodoluminescence. Chemical Geology 191, 121-140.
). Annealed zircons exhibit well-defined textures that allowed us to identify three groups (Fig. 1). The first group shows fine oscillatory zoning, with large contrasts between growth zones, that we interpreted as magmatic (Fig. 1). The second group is also interpreted as magmatic because it exhibits fine oscillatory zoning, with local sector zoning, but with very little contrast between growth zones (Fig. 1). The third group consists in irregular and/or chaotic textures that resemble metamorphic zircons (Fig. 1, Figs. S-4 to S-7; Corfu et al., 2003Corfu, F., Hanchar, J.M., Hoskin, P.W.O., Kinny, P. (2003) Atlas of zircon textures. Reviews in Mineralogy and Geochemistry 53, 469-500.
). The first and second groups are often surrounded by metamorphic overgrowths that, hence, belong to the third group (Figs. S-4 to S-7). All groups are present in Mount Sones, whereas only the first and third groups are represented in Gage Ridge.Figure 1 Cathodoluminescence images of representative crystals from Napier zircon populations with details of textures with and without annealing. This figure illustrates the CL signal enhancing effect of zircon annealing which, in turn, allows three groups to be identified based on internal textures (see text for details). Thick white bars represent 50 μm.
In both samples, zircons from group 1 are characterised by large variations in 207Pb/206Pb ages, ranging from the oldest determined (3794 ± 40 in Mount Sones and 3857 ± 39 Ma in Gage Ridge) down to about 2500 Ma, and broadly consistent initial 176Hf/177Hf around the least radiogenic values (0.2802-0.2804), except for a few data points in Gage Ridge (Fig. S-8, Table S-7). This translates into major positive correlations in ɛHf versus age diagram with all ɛHf being negative (Fig. 2). Group 2 zircons, which are only found in Mount Sones, form a coherent cluster with 207Pb/206Pb ages between 2700-2900 Ma and initial 176Hf/177Hf among the most radiogenic (0.2806-0.2808; Fig. S-8, Table S-7) despite their corresponding initial ɛHf values being all negative (Fig. 2). Group 3 zircons, contrary to group 1, show little variation in 207Pb/206Pb ages (2400-2700 Ma) but large variations in initial 176Hf/177Hf, and therefore ɛHf, that almost cover the entire range of measured values (Fig. 2). Contrary to the first two groups which exhibit Th/U values within the common igneous range (0.2-0.8; Fig. S-9; e.g., Kirkland et al., 2015
Kirkland, C.L., Smithies, R.H., Taylor, R.J.M., Evans, N., McDonald, B. (2015) Zircon Th/U ratios in magmatic environs. Lithos 212-215, 397-414.
), the third group in Mount Sones shows a great variability in Th/U (up to 2.9) in line with its metamorphic origin in granulite facies (e.g., Vavra et al., 1999Vavra, G., Schmid, R., Gebauer, D. (1999) Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite- facies zircons: geochronology of the Ivrea Zone (Southern Alps). Contributions to Mineralogy and Petrology 134, 380-404.
). Our new data comply very well with those already published (Guitreau et al., 2012Guitreau, M., Blichert-Toft, J., Martin, H., Mojzsis, S.J., Albarède, F. (2012) Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust. Earth and Planetary Science Letters 337, 211-223.
; Hiess and Bennett, 2016Hiess, J., Bennett, V.C. (2016) Chondritic Lu-Hf in the early crust-mantle system as recorded by zircon populations from the oldest Eoarchean rocks of the Yilgarn Craton, West Australia and Enderby Land, Antarctica. Chemical Geology 427, 125-143.
), as shown in Figure S-2, and allow observed patterns to be properly deconvoluted and reliably interpreted.The εHf-age pattern observed for group 1 is typical of ancient zircon populations (Fig. 2; e.g., Guitreau and Blichert-Toft, 2014
Guitreau, M., Blichert-Toft, J. (2014) Implications of discordant U-Pb ages on Hf isotope studies of detrital zircons. Chemical Geology 385, 17-25.
) which experienced metamorphism that resulted in re-opening of the U-Pb system without influencing the Lu-Hf system significantly. Therefore, we interpret group 1 as the original igneous population. The second group is also igneous and probably represents melt percolation in Mount Sones, given its similarity in timing and Hf isotope composition to Dallwitz Nunatak orthogneiss which is located between Mount Sones and Gage Ridge (Figs. S-1 and S-10; Guitreau et al., 2012Guitreau, M., Blichert-Toft, J., Martin, H., Mojzsis, S.J., Albarède, F. (2012) Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust. Earth and Planetary Science Letters 337, 211-223.
). Group 3 represents zircons that grew and/or recrystallised during long-lived Neoarchean metamorphism. Their formation likely involved in situ dissolution-reprecipitation of radiation-damaged zircons, as well as influx of radiogenic Hf from high Lu/Hf minerals (e.g., amphibole, biotite, plagioclase), thereby accounting for the large range of εHf observed. The large discrepancies between Napier zircon and whole rock initial εHf at 3.8 Ga indicate that Lu-Hf isotope systematics were disturbed at the whole rock scale during later metamorphic events, most likely around 2.5 Ga (Fig. S-10).Figure 2 ɛHf versus 207Pb/206Pb age diagrams for Mount Sones and Gage Ridge zircons. Black dashed lines represent the time-evolution of a CHUR reservoir (Iizuka et al., 2015
Iizuka, T., Yamaguchi, T., Hibiya, Y., Amelin, Y. (2015) Meteorite zircon constraints on the bulk Lu-Hf isotope composition and early differentiation of the Earth. Proceedings of the National Academy of Science 112, 5331-5336.
) formed at 4568 Ma (Bouvier and Wadhwa, 2010Bouvier, A., Wadhwa, M. (2010) The age of the Solar System redefined by the oldest Pb-Pb age of a meteoritic inclusion. Nature Geoscience 3, 637-641.
). Black dotted lines correspond to reservoirs that started with group 1 initial 176Hf/177Hf and evolved with 176Lu/177Hf ratios that are indicated on the left of the diagrams (e.g., 0.025). The values of 0.002 and 0.0016 correspond to 176Lu/177Hf measured in whole rock powders of Mount Sones and Gage Ridge orthogneisses, respectively. The grey fields encompass evolutions of Napier zircons based on highest and lowest 176Lu/177Hf measured in Mount Sones and Gage Ridge zircon populations. The general positive correlation of data for group 1 highlights typical artefacts of ancient Pb loss (e.g., Guitreau et al., 2012Guitreau, M., Blichert-Toft, J., Martin, H., Mojzsis, S.J., Albarède, F. (2012) Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust. Earth and Planetary Science Letters 337, 211-223.
). Therefore, the original Hf isotope signatures of corresponding zircon populations are indicated by the oldest (and most concordant) crystals, which happen to be sub-chondritic for both samples. Data are fully consistent between annealed and not-annealed zircons, hence, demonstrating that annealing did not influence any of the measured systematics.Our oldest ages for Mount Sones and Gage Ridge orthogneisses determined at 3794 ± 40 and 3857 ± 39 Ma, respectively, compares well with previous estimates of 3851 ± 62 Ma (Harley and Black, 1997
Harley, S.L., Black, L.P. (1997) A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies. Antarctic Science 9, 74-91.
; Kelly and Harley, 2005Kelly, N.M., Harley, S.L. (2005) An integrated microtextural and chemical approach to zircon geochronology: refining the Archaean history of the Napier Complex east Antarctica. Contributions to Mineralogy and Petrology 149, 57-84.
). The initial Hf isotope composition of group 1 zircons from Mount Sones and Gage Ridge are 0.280238 ± 0.00004 (2 s.d.; n = 23) and 0.280169 ± 0.00007 (2 s.d.; n = 7), respectively, which translates into initial ɛHf of -2.6 ± 1.5 and -3.6 ± 2.5 for Mount Sones and Gage Ridge, respectively. Therefore, our results indicate that an enriched reservoir was tapped during the formation of the protoliths to the oldest orthogneiss of the Napier craton. Major and minor element concentrations for Mount Sones suggest its derivation from a mafic crust (Fig. S-3; Black et al., 1986Black, L.P., Williams, I.S., Compston, W. (1986) Four zircon ages from one rock — the history of a 3930 Ma-old granulite from Mount Sones, Enderby Land, Antarctica. Contributions to Mineralogy and Petrology 94, 427–437.
). Gage Ridge exhibits a strong positive Eu anomaly that would indicate that it is a cumulate and, therefore, its composition no longer represents that of a liquid. Consequently, we cannot unambiguously estimate its source based on geochemistry.Coupled 147,146Sm-143,142Nd measurements provide additional constrains on the nature of this crust and the timing of its formation. Firstly, our new 147Sm-143Nd isotope data for Mount Sones are consistent with those published in Black and McCulloch (1987)
Black, L.P., McCulloch, M.T. (1987) Evidence for isotopic equilibration of Sm-Nd whole-rock systems in early Archaean crust of Enderby Land, Antarctica. Earth and Planetary Science Letters 82, 15-24.
(Fig. S-11) and give an ɛNd of -2.0 ± 0.3 at 3794 Ma, which compares well with the Hf isotope signature of group 1 zircons from this sample. Therefore, we suggest that Mount Sones exhibits a near-pristine Nd isotope signature in contrast to the arguably disturbed Sm-Nd isotope systematics in Gage Ridge. Moreover, Napier samples exhibit negative μ142Nd anomalies of -8.7 ± 3.9 for Mount Sones and -12.1 ± 6.2 for Gage Ridge (Fig. 3, Table S-9) which indicates that they both tapped an enriched reservoir that formed while 146Sm was still extant, hence, during the first 300 Myr of Solar System history. Coupled Sm-Nd isotope systematics in Mount Sones further indicate that the enriched reservoir (precursor) formed between 4456 and 4356 Ma with a 147Sm/144Nd of ~0.17 (Fig. 3) which confirms its mafic nature (e.g., O’Neil and Carlson, 2017O’Neil, J., Carlson, R.W. (2017) Building Archean cratons from Hadean mafic crust. Science 355, 1199-1202.
). Using a global compilation of coupled Lu-Hf and Sm-Nd isotope systematics to estimate the equivalent 176Lu/177Hf to a 147Sm/144Nd of 0.17 (Albarède et al., 2000Albarède, F., Blichert-Toft, J., Vervoort, J.D., Gleason, J.D., Rosing, M. (2000) Hf-Nd isotope evidence for a transient dynamic regime in the early terrestrial mantle. Nature 404, 488-490.
), we obtain a value of 0.025 which is typical of a mafic crust. Two stage CHUR Lu-Hf model ages for Group 1 zircons give ages of 4212 ± 226 Ma for Mount Sones and 4422 ± 394 Ma for Gage Ridge, which are consistent with combined 147,146Sm-143,142Nd isotope systematics (See Methods in Supplementary Information). Our new results on Mount Sones and Gage Ridge orthogneisses, therefore, demonstrate that a very old Hadean mafic protocrust was reworked during the formation of the Napier craton.Figure 3 Coupled 146Sm-142Nd and 147Sm-143Nd plot showing the data obtained for Mount Sones orthogneiss (78285007) as well as the coupled evolution of μ142Nd and ɛ143Nd signatures for lithologies with various Sm/Nd ratios. Solid lines represent isochrons with respective ages indicated by ∆T, which means time after 4568 Ma. Dashed curves correspond to the coupled evolution of μ142Nd and ɛ143Nd signatures according to specific 147Sm/144Nd values that are indicated next to the curves (i.e. 0.14-0.19). Mount Sones μ142Nd and ɛ143Nd isotope signatures are compatible with a mafic source (147Sm/144Nd = 0.17) that separated from a reservoir with a chondritic REE pattern ~150 Myr after Solar System formation (i.e. ~4400 Myr ago). Here we assume that the initial 142Nd/144Nd ratio of the Earth is similar to that measured in the modern terrestrial mantle (μ142Nd = 0), which is equivalent to the signature measured in enstatite chondrites from the EL sub-group (Boyet et al., 2018
Boyet, M., Bouvier, A., Frossard, P., Hammouda, T., Garçon, M., Gannoun, A. (2018) Enstatite chondrites EL3 as building blocks for the Earth: the debate over the 146Sm-142Nd systematics. Earth and Planetary Science Letters 488, 68-78.
).Our conclusion echoes similar scenarios that have been proposed for other Archean terranes worldwide such as the Itsaq Gneiss Complex (Greenland; Kamber et al., 2003
Kamber, B.S., Collerson, K.D., Moorbath, S., Whitehouse, M.J. (2003) Inheritance of early Archaean Pb-isotope variability from long-lived Hadean protocrust. Contributions to Mineralogy and Petrology 145, 25-46.
; Kemp et al., 2019Kemp, A.I.S., Whitehouse, M.J., Vervoort, J.D. (2019) Deciphering the zircon Hf isotope systematics of Eoarchean gneisses from Greenland: Implications for ancient crust-mantle differentiation and Pb isotope controversies. Geochimica et Cosmochimica Acta 250, 76-97.
), the Acasta Gneiss Complex (Canada; e.g., Guitreau et al., 2014Guitreau, M., Blichert-Toft, J., Mojzsis, S.J., Roth, A.S.G., Bourdon, B., Cates, N.L., Bleeker, W. (2014) Lu-Hf isotope systematics of the Hadean-Eoarchean Acasta Gneiss Complex (Northwest Territories, Canada). Geochimica et Cosmochimica Acta 135, 251-269.
; Roth et al., 2014Roth, A.S.G., Bourdon, B., Mojzsis, S.J., Rudge, J.F., Guitreau, M., Blichert-Toft, J. (2014) Combined 147,146Sm-143,142Nd constraints on the longevity and residence time of early terrestrial crust. G-Cubed 15, 1-17.
; Reimink et al., 2018Reimink, J.R., Chacko, T., Carlson, R.W., Shirey, S.B., Liu, J., Stern, R.A., Bauer, A.M., Pearson, D.G., Heaman, L.M. (2018) Petrogenesis and tectonics of the Acasta Gneiss >Complex derived from integrated petrology and 142Nd and 182W extinct nuclide-geochemistry. Earth and Planetary Science Letters 494, 12-22.
), the Nuvvuagittuq Supracrustal Belt (Canada; e.g., O’Neil and Carlson, 2017O’Neil, J., Carlson, R.W. (2017) Building Archean cratons from Hadean mafic crust. Science 355, 1199-1202.
; Caro et al., 2017Caro, G., Morino, P., Mojzsis, S.J., Cates, N.L., Bleeker, W. (2017) Sluggish Hadean geodynamics: Evidence from coupled 146,147Sm-142,143Nd systematics in Eoarchean supracrustal rocks of the Inukjuak domain (Québec). Earth and Planetary Science Letters 457, 23-37.
), and the North China craton (Li et al., 2017Li, C.-F., Wang, X.C., Wilde, S., Li, X.H., Wang, Y.F., Li, F. (2017) Differentiation of the early silicate Earth as recorded by 142Nd-143Nd in 3.8-3.0 Ga rocks from the Anshan Complex, North China craton. Precambrian Research 301, 86-101.
). Therefore, we propose that Hadean protocrusts (and proto-continents) were massively reworked at the Hadean-Eoarchean boundary in order to account for both the absence of Hadean crust in the present day and its little influence throughout the Archean (e.g., Guitreau et al., 2012Guitreau, M., Blichert-Toft, J., Martin, H., Mojzsis, S.J., Albarède, F. (2012) Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust. Earth and Planetary Science Letters 337, 211-223.
; Roth et al., 2014Roth, A.S.G., Bourdon, B., Mojzsis, S.J., Rudge, J.F., Guitreau, M., Blichert-Toft, J. (2014) Combined 147,146Sm-143,142Nd constraints on the longevity and residence time of early terrestrial crust. G-Cubed 15, 1-17.
; Kemp et al., 2015Kemp, A.I.S., Hickman, A.H., Kirkland, C.L., Vervoort, J.D. (2015) Hf isotopes in detrital and inherited zircons of the Pilbara Craton provide no evidence for Hadean continents. Precambrian Research 261, 112-126.
) despite recent models proposing that crustal growth was rapid in the Hadean and Eoarchean (~25 % of present-day volume or surface Belousova et al., 2010Belousova, E.A., Kostitsyn, Y.A., Griffin, W.L., Begg, G.C., O’Reilly, S.Y., Pearson, N.J. (2010) The growth of the continental crust: constraints from zircon Hf-isotope data. Lithos 119, 457-466.
; Dhuime et al., 2012Dhuime, B., Hawkesworth, C.J., Cawood, P.A., Storey, C. (2012) A change in the geodynamics of continental growth 3 billion years ago. Science 335, 1334-1336.
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Acknowledgements
Chris Carson and Geoscience Australia are thanked for providing the Napier Complex samples. Anne-Magali Seydoux-Guillaume is thanked for discussions about zircon crystallography and imaging. MG acknowledges financial support from LabEx ClerVolc (ANR-10-LABX-0006), Région Auvergne, the European Regional Development Fund, and the French Agence Nationale de la Recherche (ANR) through the funded project Zircontinents (ANR-17-CE31-0021). MB acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement N° 682778 and from the French Government Laboratory of Excellence initiative n°ANR-10-LABX-0006. This is Laboratory of Excellence ClerVolc contribution number 376. Last but not least, we thank Ambre Luguet for efficient editorial handling and N. Alex Zirakparvar and Fernando Corfu for constructive reviews that helped improve the present manuscript.
Editor: Ambre Luguet
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References
Albarède, F., Blichert-Toft, J., Vervoort, J.D., Gleason, J.D., Rosing, M. (2000) Hf-Nd isotope evidence for a transient dynamic regime in the early terrestrial mantle. Nature 404, 488-490.
Show in contextUsing a global compilation of coupled Lu-Hf and Sm-Nd isotope systematics to estimate the equivalent 176Lu/177Hf to a 147Sm/144Nd of 0.17 (Albarède et al., 2000), we obtain a value of 0.025 which is typical of a mafic crust.
View in article
Belousova, E.A., Kostitsyn, Y.A., Griffin, W.L., Begg, G.C., O’Reilly, S.Y., Pearson, N.J. (2010) The growth of the continental crust: constraints from zircon Hf-isotope data. Lithos 119, 457-466.
Show in contextTherefore, we propose that Hadean protocrusts (and proto-continents) were massively reworked at the Hadean-Eoarchean boundary in order to account for both the absence of Hadean crust in the present day and its little influence throughout the Archean (e.g., Guitreau et al., 2012; Roth et al., 2014; Kemp et al., 2015) despite recent models proposing that crustal growth was rapid in the Hadean and Eoarchean (~25 % of present-day volume or surface Belousova et al., 2010; Dhuime et al., 2012).
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Black, L.P., McCulloch, M.T. (1987) Evidence for isotopic equilibration of Sm-Nd whole-rock systems in early Archaean crust of Enderby Land, Antarctica. Earth and Planetary Science Letters 82, 15-24.
Show in contextConsequently, radiogenic isotope systematics (e.g., Rb-Sr, Sm-Nd) were severely disturbed in most samples (e.g., Black and McCulloch, 1987).
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Firstly, our new 147Sm-143Nd isotope data for Mount Sones are consistent with those published in Black and McCulloch (1987) (Fig. S-11) and give an ɛNd of -2.0 ± 0.3 at 3794 Ma, which compares well with the Hf isotope signature of group 1 zircons from this sample.
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Black, L.P., Williams, I.S., Compston, W. (1986) Four zircon ages from one rock — the history of a 3930 Ma-old granulite from Mount Sones, Enderby Land, Antarctica. Contributions to Mineralogy and Petrology 94, 427–437.
Show in context The Napier complex (East Antarctica) is one of the few Archean terranes that contain some of Earth’s oldest rocks (Black et al., 1986; Fig. S-1).
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These grains show a greater complexity than commonly seen in ancient zircons (Williams et al., 1984; Black et al., 1986; Guitreau et al., 2012; Kusiak et al., 2013; Hiess and Bennett, 2016) and deconvoluting original igneous signatures from metamorphic overprints remains challenging.
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They are among the oldest rocks from this area (Black et al., 1986; Harley and Black, 1997).
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Mount Sones exhibits chemical composition identical to that of typical Archean tonalite-trondhjemite-granodiorite (TTG) suites (e.g., high Na2O/K2O, high Sr/Y, fractionated REE patterns; Moyen and Martin, 2012) with a normative composition intermediate between tonalite and trondhjemite (Black et al., 1986; Fig. S-3).
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Major and minor element concentrations for Mount Sones suggest its derivation from a mafic crust (Fig. S-3; Black et al., 1986).
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Bouvier, A., Wadhwa, M. (2010) The age of the Solar System redefined by the oldest Pb-Pb age of a meteoritic inclusion. Nature Geoscience 3, 637-641.
Show in context Figure 2 [...] Black dashed lines represent the time-evolution of a CHUR reservoir (Iizuka et al., 2015) formed at 4568 Ma (Bouvier and Wadhwa, 2010).
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Boyet, M., Bouvier, A., Frossard, P., Hammouda, T., Garçon, M., Gannoun, A. (2018) Enstatite chondrites EL3 as building blocks for the Earth: the debate over the 146Sm-142Nd systematics. Earth and Planetary Science Letters 488, 68-78.
Show in context Figure 3 [...] Here we assume that the initial 142Nd/144Nd ratio of the Earth is similar to that measured in the modern terrestrial mantle (μ142Nd = 0), which is equivalent to the signature measured in enstatite chondrites from the EL sub-group (Boyet et al., 2018).
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Caro, G., Morino, P., Mojzsis, S.J., Cates, N.L., Bleeker, W. (2017) Sluggish Hadean geodynamics: Evidence from coupled 146,147Sm-142,143Nd systematics in Eoarchean supracrustal rocks of the Inukjuak domain (Québec). Earth and Planetary Science Letters 457, 23-37.
Show in context Our conclusion echoes similar scenarios that have been proposed for other Archean terranes worldwide such as the Itsaq Gneiss Complex (Greenland; Kamber et al., 2003; Kemp et al., 2019), the Acasta Gneiss Complex (Canada; e.g., Guitreau et al., 2014; Roth et al., 2014; Reimink et al., 2018), the Nuvvuagittuq Supracrustal Belt (Canada; e.g., O’Neil and Carlson, 2017; Caro et al., 2017), and the North China craton (Li et al., 2017).
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Condie, K. (2007) The distribution of Paleoarchean crust. In: Van Kranendonk, M.J., Smithies, R.H., Bennett, V.C. (Eds.) Earth’s Oldest Rocks. First Edition, Elsevier, Amsterdam, 9-18.
Show in context The small number of localities hosting >3.7 Ga rocks, together with the absence of Hadean rocks from the geological record, is a limitation for our understanding of the early evolution of the Earth and the origin of the first continents (e.g., Condie, 2007).
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Corfu, F., Hanchar, J.M., Hoskin, P.W.O., Kinny, P. (2003) Atlas of zircon textures. Reviews in Mineralogy and Geochemistry 53, 469-500.
Show in context The third group consists in irregular and/or chaotic textures that resemble metamorphic zircons (Fig. 1, Figs. S-4 to S-7; Corfu et al., 2003).
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Dhuime, B., Hawkesworth, C.J., Cawood, P.A., Storey, C. (2012) A change in the geodynamics of continental growth 3 billion years ago. Science 335, 1334-1336.
Show in context Therefore, we propose that Hadean protocrusts (and proto-continents) were massively reworked at the Hadean-Eoarchean boundary in order to account for both the absence of Hadean crust in the present day and its little influence throughout the Archean (e.g., Guitreau et al., 2012; Roth et al., 2014; Kemp et al., 2015) despite recent models proposing that crustal growth was rapid in the Hadean and Eoarchean (~25 % of present-day volume or surface Belousova et al., 2010; Dhuime et al., 2012).
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Guitreau, M., Blichert-Toft, J. (2014) Implications of discordant U-Pb ages on Hf isotope studies of detrital zircons. Chemical Geology 385, 17-25.
Show in context The εHf-age pattern observed for group 1 is typical of ancient zircon populations (Fig. 2; e.g., Guitreau and Blichert-Toft, 2014) which experienced metamorphism that resulted in re-opening of the U-Pb system without influencing the Lu-Hf system significantly.
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Guitreau, M., Blichert-Toft, J., Martin, H., Mojzsis, S.J., Albarède, F. (2012) Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust. Earth and Planetary Science Letters 337, 211-223.
Show in context These grains show a greater complexity than commonly seen in ancient zircons (Williams et al., 1984; Black et al., 1986; Guitreau et al., 2012; Kusiak et al., 2013; Hiess and Bennett, 2016) and deconvoluting original igneous signatures from metamorphic overprints remains challenging.
View in article
Our new data comply very well with those already published (Guitreau et al., 2012; Hiess and Bennett, 2016), as shown in Figure S-2, and allow observed patterns to be properly deconvoluted and reliably interpreted.
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The second group is also igneous and probably represents melt percolation in Mount Sones, given its similarity in timing and Hf isotope composition to Dallwitz Nunatak orthogneiss which is located between Mount Sones and Gage Ridge (Figs. S-1 and S-10; Guitreau et al., 2012).
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Figure 2 [...] The general positive correlation of data for group 1 highlights typical artefacts of ancient Pb loss (e.g., Guitreau et al., 2012).
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Therefore, we propose that Hadean protocrusts (and proto-continents) were massively reworked at the Hadean-Eoarchean boundary in order to account for both the absence of Hadean crust in the present day and its little influence throughout the Archean (e.g., Guitreau et al., 2012; Roth et al., 2014; Kemp et al., 2015) despite recent models proposing that crustal growth was rapid in the Hadean and Eoarchean (~25 % of present-day volume or surface Belousova et al., 2010; Dhuime et al., 2012).
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Guitreau, M., Blichert-Toft, J., Mojzsis, S.J., Roth, A.S.G., Bourdon, B., Cates, N.L., Bleeker, W. (2014) Lu-Hf isotope systematics of the Hadean-Eoarchean Acasta Gneiss Complex (Northwest Territories, Canada). Geochimica et Cosmochimica Acta 135, 251-269.
Show in context Our conclusion echoes similar scenarios that have been proposed for other Archean terranes worldwide such as the Itsaq Gneiss Complex (Greenland; Kamber et al., 2003; Kemp et al., 2019), the Acasta Gneiss Complex (Canada; e.g., Guitreau et al., 2014; Roth et al., 2014; Reimink et al., 2018), the Nuvvuagittuq Supracrustal Belt (Canada; e.g., O’Neil and Carlson, 2017; Caro et al., 2017), and the North China craton (Li et al., 2017).
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Guitreau, M., Mora, N., Paquette, J.-L. (2018) Crystallization and disturbance histories of single zircon crystals from Hadean-Eoarchean Acasta gneisses examined by LA-ICP-MS U-Pb traverses. G-Cubed 19, 272-291.
Show in context Here we combine cathodoluminescence (CL) and back scattered electron (BSE) images with U-Pb age profiles by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in zircons from two Napier orthogneisses, following the procedure outlined in Guitreau et al. (2018).
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Harley, S.L., Black, L.P. (1997) A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies. Antarctic Science 9, 74-91.
Show in context They are among the oldest rocks from this area (Black et al., 1986; Harley and Black, 1997).
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Gage Ridge has a composition closer to that of granite (Harley and Black, 1997) despite a strongly fractionated REE pattern with a pronounced positive Eu anomaly suggesting that it is likely a cumulate from a TTG melt (Fig. S-3).
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Our oldest ages for Mount Sones and Gage Ridge orthogneisses determined at 3794 ± 40 and 3857 ± 39 Ma, respectively, compares well with previous estimates of 3851 ± 62 Ma (Harley and Black, 1997; Kelly and Harley, 2005).
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Harley, S.L., Motoyoshi, Y. (2000) Al zoning in orthopyroxene in a sapphirine quartzite: evidence for >1120°C UHT metamorphism in the Napier Complex, Antarctica, and implications for the entropy of sapphirine. Contributions to Mineralogy and Petrology 138, 293-307.
Show in contextThis complex recorded Meso- and Neoarchean metamorphism that reached extreme conditions corresponding to granulite facies at 2.5 Ga (1050-1120 °C and 7-11 kbar; Table S-1) (Harley and Motoyoshi, 2000).
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Hiess, J., Bennett, V.C. (2016) Chondritic Lu-Hf in the early crust-mantle system as recorded by zircon populations from the oldest Eoarchean rocks of the Yilgarn Craton, West Australia and Enderby Land, Antarctica. Chemical Geology 427, 125-143.
Show in contextThese grains show a greater complexity than commonly seen in ancient zircons (Williams et al., 1984; Black et al., 1986; Guitreau et al., 2012; Kusiak et al., 2013; Hiess and Bennett, 2016) and deconvoluting original igneous signatures from metamorphic overprints remains challenging.
View in article
Our new data comply very well with those already published (Guitreau et al., 2012; Hiess and Bennett, 2016), as shown in Figure S-2, and allow observed patterns to be properly deconvoluted and reliably interpreted.
View in article
Iizuka, T., Yamaguchi, T., Hibiya, Y., Amelin, Y. (2015) Meteorite zircon constraints on the bulk Lu-Hf isotope composition and early differentiation of the Earth. Proceedings of the National Academy of Science 112, 5331-5336.
Show in context Figure 2 [...] Black dashed lines represent the time-evolution of a CHUR reservoir (Iizuka et al., 2015) formed at 4568 Ma (Bouvier and Wadhwa, 2010).
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Kamber, B.S., Collerson, K.D., Moorbath, S., Whitehouse, M.J. (2003) Inheritance of early Archaean Pb-isotope variability from long-lived Hadean protocrust. Contributions to Mineralogy and Petrology 145, 25-46.
Show in contextOur conclusion echoes similar scenarios that have been proposed for other Archean terranes worldwide such as the Itsaq Gneiss Complex (Greenland; Kamber et al., 2003; Kemp et al., 2019), the Acasta Gneiss Complex (Canada; e.g., Guitreau et al., 2014; Roth et al., 2014; Reimink et al., 2018), the Nuvvuagittuq Supracrustal Belt (Canada; e.g., O’Neil and Carlson, 2017; Caro et al., 2017), and the North China craton (Li et al., 2017).
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Kelly, N.M., Harley, S.L. (2005) An integrated microtextural and chemical approach to zircon geochronology: refining the Archaean history of the Napier Complex east Antarctica. Contributions to Mineralogy and Petrology 149, 57-84.
Show in context Metamorphic events were recorded in zircon crystals that sometimes also preserved information about original crystallisation (Kelly and Harley, 2005).
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Our oldest ages for Mount Sones and Gage Ridge orthogneisses determined at 3794 ± 40 and 3857 ± 39 Ma, respectively, compares well with previous estimates of 3851 ± 62 Ma (Harley and Black, 1997; Kelly and Harley, 2005).
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Kemp, A.I.S., Hickman, A.H., Kirkland, C.L., Vervoort, J.D. (2015) Hf isotopes in detrital and inherited zircons of the Pilbara Craton provide no evidence for Hadean continents. Precambrian Research 261, 112-126.
Show in contextTherefore, we propose that Hadean protocrusts (and proto-continents) were massively reworked at the Hadean-Eoarchean boundary in order to account for both the absence of Hadean crust in the present day and its little influence throughout the Archean (e.g., Guitreau et al., 2012; Roth et al., 2014; Kemp et al., 2015) despite recent models proposing that crustal growth was rapid in the Hadean and Eoarchean (~25 % of present-day volume or surface Belousova et al., 2010; Dhuime et al., 2012).
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Kemp, A.I.S., Whitehouse, M.J., Vervoort, J.D. (2019) Deciphering the zircon Hf isotope systematics of Eoarchean gneisses from Greenland: Implications for ancient crust-mantle differentiation and Pb isotope controversies. Geochimica et Cosmochimica Acta 250, 76-97.
Show in contextOur conclusion echoes similar scenarios that have been proposed for other Archean terranes worldwide such as the Itsaq Gneiss Complex (Greenland; Kamber et al., 2003; Kemp et al., 2019), the Acasta Gneiss Complex (Canada; e.g., Guitreau et al., 2014; Roth et al., 2014; Reimink et al., 2018), the Nuvvuagittuq Supracrustal Belt (Canada; e.g., O’Neil and Carlson, 2017; Caro et al., 2017), and the North China craton (Li et al., 2017).
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Kirkland, C.L., Smithies, R.H., Taylor, R.J.M., Evans, N., McDonald, B. (2015) Zircon Th/U ratios in magmatic environs. Lithos 212-215, 397-414.
Show in context Contrary to the first two groups which exhibit Th/U values within the common igneous range (0.2-0.8; Fig. S-9; e.g., Kirkland et al., 2015), the third group in Mount Sones shows a great variability in Th/U (up to 2.9) in line with its metamorphic origin in granulite facies (e.g., Vavra et al., 1999).
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Kusiak, M.A., Whitehouse, M.J., Wilde, S.A., Nemchin, A.A., Clark, C. (2013) Mobilization of radiogenic Pb in zircon revealed by ion imaging: implications for early Earth geochronology. Geology 41, 291–294.
Show in context These grains show a greater complexity than commonly seen in ancient zircons (Williams et al., 1984; Black et al., 1986; Guitreau et al., 2012; Kusiak et al., 2013; Hiess and Bennett, 2016) and deconvoluting original igneous signatures from metamorphic overprints remains challenging.
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Napier zircon crystals have experienced a complex geological history which is difficult to decipher given their high U and Th concentrations that are responsible for the faint signals in CL images (e.g., Kusiak et al., 2013).
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Li, C.-F., Wang, X.C., Wilde, S., Li, X.H., Wang, Y.F., Li, F. (2017) Differentiation of the early silicate Earth as recorded by 142Nd-143Nd in 3.8-3.0 Ga rocks from the Anshan Complex, North China craton. Precambrian Research 301, 86-101.
Show in contextOur conclusion echoes similar scenarios that have been proposed for other Archean terranes worldwide such as the Itsaq Gneiss Complex (Greenland; Kamber et al., 2003; Kemp et al., 2019), the Acasta Gneiss Complex (Canada; e.g., Guitreau et al., 2014; Roth et al., 2014; Reimink et al., 2018), the Nuvvuagittuq Supracrustal Belt (Canada; e.g., O’Neil and Carlson, 2017; Caro et al., 2017), and the North China craton (Li et al., 2017).
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Moyen, J.-F., Martin, H. (2012) Forty years of TTG research. Lithos 148, 312-336.
Show in context Mount Sones exhibits chemical composition identical to that of typical Archean tonalite-trondhjemite-granodiorite (TTG) suites (e.g., high Na2O/K2O, high Sr/Y, fractionated REE patterns; Moyen and Martin, 2012) with a normative composition intermediate between tonalite and trondhjemite (Black et al., 1986; Fig. S-3).
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Nasdala, L., Lengauer, C.L., Hanchar, J.M., Kronz, A., Wirth, R., Blanc, P., Kennedy, A.K., Seydoux-Guillaume, A.-M. (2002) Annealing radiation damage and the recovery of cathodoluminescence. Chemical Geology 191, 121-140.
Show in contextWe performed annealing on a subset of zircon crystals (850 °C for 48 hr) because this thermal process increases the intensity of the CL signal (Nasdala et al., 2002).
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O’Neil, J., Carlson, R.W. (2017) Building Archean cratons from Hadean mafic crust. Science 355, 1199-1202.
Show in context Coupled Sm-Nd isotope systematics in Mount Sones further indicate that the enriched reservoir (precursor) formed between 4456 and 4356 Ma with a 147Sm/144Nd of ~0.17 (Fig. 3) which confirms its mafic nature (e.g., O’Neil and Carlson, 2017).
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Our conclusion echoes similar scenarios that have been proposed for other Archean terranes worldwide such as the Itsaq Gneiss Complex (Greenland; Kamber et al., 2003; Kemp et al., 2019), the Acasta Gneiss Complex (Canada; e.g., Guitreau et al., 2014; Roth et al., 2014; Reimink et al., 2018), the Nuvvuagittuq Supracrustal Belt (Canada; e.g., O’Neil and Carlson, 2017; Caro et al., 2017), and the North China craton (Li et al., 2017).
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Reimink, J.R., Chacko, T., Carlson, R.W., Shirey, S.B., Liu, J., Stern, R.A., Bauer, A.M., Pearson, D.G., Heaman, L.M. (2018) Petrogenesis and tectonics of the Acasta Gneiss >Complex derived from integrated petrology and 142Nd and 182W extinct nuclide-geochemistry. Earth and Planetary Science Letters 494, 12-22.
Show in contextOur conclusion echoes similar scenarios that have been proposed for other Archean terranes worldwide such as the Itsaq Gneiss Complex (Greenland; Kamber et al., 2003; Kemp et al., 2019), the Acasta Gneiss Complex (Canada; e.g., Guitreau et al., 2014; Roth et al., 2014; Reimink et al., 2018), the Nuvvuagittuq Supracrustal Belt (Canada; e.g., O’Neil and Carlson, 2017; Caro et al., 2017), and the North China craton (Li et al., 2017).
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Roth, A.S.G., Bourdon, B., Mojzsis, S.J., Rudge, J.F., Guitreau, M., Blichert-Toft, J. (2014) Combined 147,146Sm-143,142Nd constraints on the longevity and residence time of early terrestrial crust. G-Cubed 15, 1-17.
Show in contextOur conclusion echoes similar scenarios that have been proposed for other Archean terranes worldwide such as the Itsaq Gneiss Complex (Greenland; Kamber et al., 2003; Kemp et al., 2019), the Acasta Gneiss Complex (Canada; e.g., Guitreau et al., 2014; Roth et al., 2014; Reimink et al., 2018), the Nuvvuagittuq Supracrustal Belt (Canada; e.g., O’Neil and Carlson, 2017; Caro et al., 2017), and the North China craton (Li et al., 2017).
View in article
Therefore, we propose that Hadean protocrusts (and proto-continents) were massively reworked at the Hadean-Eoarchean boundary in order to account for both the absence of Hadean crust in the present day and its little influence throughout the Archean (e.g., Guitreau et al., 2012; Roth et al., 2014; Kemp et al., 2015) despite recent models proposing that crustal growth was rapid in the Hadean and Eoarchean (~25 % of present-day volume or surface Belousova et al., 2010; Dhuime et al., 2012).
View in article
Vavra, G., Schmid, R., Gebauer, D. (1999) Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite- facies zircons: geochronology of the Ivrea Zone (Southern Alps). Contributions to Mineralogy and Petrology 134, 380-404.
Show in context Contrary to the first two groups which exhibit Th/U values within the common igneous range (0.2-0.8; Fig. S-9; e.g., Kirkland et al., 2015), the third group in Mount Sones shows a great variability in Th/U (up to 2.9) in line with its metamorphic origin in granulite facies (e.g., Vavra et al., 1999).
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Williams, I.S., Compston, W., Black, L.P., Ireland, T.R., Foster, J.J. (1984) Unsupported radiogenic Pb in zircon: a cause of anomalously high Pb-Pb, U-Pb and Th-Pb ages. Contributions to Mineralogy and Petrology 88, 322-327.
Show in context These grains show a greater complexity than commonly seen in ancient zircons (Williams et al., 1984; Black et al., 1986; Guitreau et al., 2012; Kusiak et al., 2013; Hiess and Bennett, 2016) and deconvoluting original igneous signatures from metamorphic overprints remains challenging.
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Supplementary Information
The Supplementary Information includes:
- Sample Description
- Methods
- Tables S-1 to S-10
- Figures S-1 to S-15
- Supplementary Information References
Download the Supplementary Information (PDF).
Download Tables S-1 to S-10 (Excel).
Figures and Tables
Figure 1 Cathodoluminescence images of representative crystals from Napier zircon populations with details of textures with and without annealing. This figure illustrates the CL signal enhancing effect of zircon annealing which, in turn, allows three groups to be identified based on internal textures (see text for details). Thick white bars represent 50 μm.
Figure 2 ɛHf versus 207Pb/206Pb age diagrams for Mount Sones and Gage Ridge zircons. Black dashed lines represent the time-evolution of a CHUR reservoir (Iizuka et al., 2015
Iizuka, T., Yamaguchi, T., Hibiya, Y., Amelin, Y. (2015) Meteorite zircon constraints on the bulk Lu-Hf isotope composition and early differentiation of the Earth. Proceedings of the National Academy of Science 112, 5331-5336.
) formed at 4568 Ma (Bouvier and Wadhwa, 2010Bouvier, A., Wadhwa, M. (2010) The age of the Solar System redefined by the oldest Pb-Pb age of a meteoritic inclusion. Nature Geoscience 3, 637-641.
). Black dotted lines correspond to reservoirs that started with group 1 initial 176Hf/177Hf and evolved with 176Lu/177Hf ratios that are indicated on the left of the diagrams (e.g., 0.025). The values of 0.002 and 0.0016 correspond to 176Lu/177Hf measured in whole rock powders of Mount Sones and Gage Ridge orthogneisses, respectively. The grey fields encompass evolutions of Napier zircons based on highest and lowest 176Lu/177Hf measured in Mount Sones and Gage Ridge zircon populations. The general positive correlation of data for group 1 highlights typical artefacts of ancient Pb loss (e.g., Guitreau et al., 2012Guitreau, M., Blichert-Toft, J., Martin, H., Mojzsis, S.J., Albarède, F. (2012) Hafnium isotope evidence from Archean granitic rocks for deep-mantle origin of continental crust. Earth and Planetary Science Letters 337, 211-223.
). Therefore, the original Hf isotope signatures of corresponding zircon populations are indicated by the oldest (and most concordant) crystals, which happen to be sub-chondritic for both samples. Data are fully consistent between annealed and not-annealed zircons, hence, demonstrating that annealing did not influence any of the measured systematics.
Figure 3 Coupled 146Sm-142Nd and 147Sm-143Nd plot showing the data obtained for Mount Sones orthogneiss (78285007) as well as the coupled evolution of μ142Nd and ɛ143Nd signatures for lithologies with various Sm/Nd ratios. Solid lines represent isochrons with respective ages indicated by ∆T, which means time after 4568 Ma. Dashed curves correspond to the coupled evolution of μ142Nd and ɛ143Nd signatures according to specific 147Sm/144Nd values that are indicated next to the curves (i.e. 0.14-0.19). Mount Sones μ142Nd and ɛ143Nd isotope signatures are compatible with a mafic source (147Sm/144Nd = 0.17) that separated from a reservoir with a chondritic REE pattern ~150 Myr after Solar System formation (i.e. ~4400 Myr ago). Here we assume that the initial 142Nd/144Nd ratio of the Earth is similar to that measured in the modern terrestrial mantle (μ142Nd = 0), which is equivalent to the signature measured in enstatite chondrites from the EL sub-group (Boyet et al., 2018
Boyet, M., Bouvier, A., Frossard, P., Hammouda, T., Garçon, M., Gannoun, A. (2018) Enstatite chondrites EL3 as building blocks for the Earth: the debate over the 146Sm-142Nd systematics. Earth and Planetary Science Letters 488, 68-78.
).